La139 NMR investigation of the interplay between lattice, charge, and spin dynamics in the charge-ordered high-Tc cuprate La1.875Ba0.125CuO4

We investigate the interplay between the lattice, charge, and spin dynamics in charge-ordered high ${T}_{c}$ cuprate ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_{4}\phantom{\rule{4pt}{0ex}}({T}_{c}=4\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ based on the inverse Laplace transform (ILT) analysis of the $^{139}\mathrm{La}$ nuclear spin-lattice relaxation rate $1/{T}_{1}$ (dubbed ${\mathrm{ILTT}}_{1}$ analysis hereafter). A major thrust of the ${\mathrm{ILTT}}_{1}$ analysis is that one can deduce the probability density function $P(1/{T}_{1})$ of distributed $1/{T}_{1}$. We demonstrate that $1/{T}_{1}^{\text{lm}}$, defined as the log mean (i.e., the center of gravity on a logarithmic scale) of $P(1/{T}_{1})$, can be well approximated by $1/{T}_{1}^{\text{str}}$ deduced from the phenomenological stretched fit; however, $P(1/{T}_{1})$ can provide much richer insight into how the lattice, charge, and spin fluctuations and their distribution develop near and below the long-range charge order at ${T}_{\text{charge}}\ensuremath{\sim}54\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Upon entering the charge-ordered state, a divergent increase of $1/{T}_{1}^{\text{lm}}$ toward the spin ordering at ${T}_{\text{spin}}^{\ensuremath{\mu}\text{SR}}\ensuremath{\simeq}35\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is accompanied by an asymmetric broadening of $P(1/{T}_{1})$. Even deep inside the charge-ordered state, $1/{T}_{1}$ at a gradually diminishing fraction of $^{139}\mathrm{La}$ sites continues to slow down as temperature is lowered, as expected for canonical superconducting ${\mathrm{CuO}}_{2}$ planes without enhanced spin fluctuations. The fraction of such canonical $^{139}\mathrm{La}$ sites almost disappears by $\ensuremath{\simeq}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. In contrast, nearly half of the $^{139}\mathrm{La}$ sites in ${\mathrm{La}}_{1.885}{\mathrm{Sr}}_{0.115}{\mathrm{CuO}}_{4}\phantom{\rule{4pt}{0ex}}({T}_{\text{charge}}\ensuremath{\simeq}80\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ still exhibit the canonical behavior without enhanced spin fluctuations even near its ${T}_{c}=31\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These contrasting behaviors explain why superconductivity in ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_{4}$ is more strongly suppressed than in ${\mathrm{La}}_{1.885}{\mathrm{Sr}}_{0.115}{\mathrm{CuO}}_{4}$ despite the lower onset temperature of the charge order.